The present invention relates to a sewing machine capable of sewing buttonholes, particularly eyelet-end buttonholes or the like having a circular stitching part.
In sewing an eyelet-end buttonhole, it is preferred that its circular stitching part be formed with a proper density of stitches or without excess or deficiency of stitches, i.e., a constant thread density so as to give a neat, beautiful appearance. In a buttonhole sewing machine known in the art, however, the number of stitches formed in the circular stitching part of a buttonhole is limited. This limitation has presented a drawback that a change in thickness of a thread to be used will cause a variation in density of stitches in such circular stitching part, i.e., the use of a thick thread will cause the stitches to be too close together while the use of a fine thread will cause the stitching part to appear scanty of stitches.
In a sewing machine using cams adapted to form various stitching patterns, on the other hand, it is possible to utilize such cams of different profiles depending upon specific thicknesses of threads and sizes of buttonholes in order to form a circular stitching part of the buttonhole having a neat appearance with a proper stitch density. In this instance, the formation of different patterns of buttonholes will require time-consuming and cumbersome changeover as well as preparation of many different cams, thereby providing another drawback of increased cost and reduced efficiency of buttonhole sewing.